[PATCH 6/6] migration: support picking vmstate disk in QMP snapshot commands

[Daniel P . Berrangé]

This wires up support for a new "vmstate" parameter to the QMP commands
for snapshots (savevm, loadvm). This parameter accepts block driver
state node name.

One use case for this would be a VM using OVMF firmware where the
variables store is the first snapshottable disk image. The vmstate
snapshot usually wants to be stored in the primary root disk of the
VM, not the firmeware varstore. Thus there needs to be a mechanism
to override the default choice of disk.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/migration/snapshot.h |  8 ++++++--
 migration/savevm.c           | 16 ++++++++++------
 monitor/hmp-cmds.c           |  6 ++++--
 qapi/migration.json          |  6 ++++++
 replay/replay-snapshot.c     |  4 ++--
 softmmu/vl.c                 |  2 +-
 6 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/include/migration/snapshot.h b/include/migration/snapshot.h
index dffb84dbe5..721147d3c1 100644
--- a/include/migration/snapshot.h
+++ b/include/migration/snapshot.h
@@ -17,7 +17,11 @@
 
 #include "qapi/qapi-builtin-types.h"
 
-int save_snapshot(const char *name, strList *exclude, Error **errp);
-int load_snapshot(const char *name, strList *exclude, Error **errp);
+int save_snapshot(const char *name,
+                  const char *vmstate, strList *exclude,
+                  Error **errp);
+int load_snapshot(const char *name,
+                  const char *vmstate, strList *exclude,
+                  Error **errp);
 
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index 4b040676f7..5fd593e475 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2624,7 +2624,8 @@ int qemu_load_device_state(QEMUFile *f)
     return 0;
 }
 
-int save_snapshot(const char *name, strList *exclude, Error **errp)
+int save_snapshot(const char *name, const char *vmstate,
+                  strList *exclude, Error **errp)
 {
     BlockDriverState *bs, *bs1;
     QEMUSnapshotInfo sn1, *sn = &sn1, old_sn1, *old_sn = &old_sn1;
@@ -2662,7 +2663,7 @@ int save_snapshot(const char *name, strList *exclude, 
Error **errp)
         }
     }
 
-    bs = bdrv_all_find_vmstate_bs(NULL, exclude, errp);
+    bs = bdrv_all_find_vmstate_bs(vmstate, exclude, errp);
     if (bs == NULL) {
         return ret;
     }
@@ -2827,7 +2828,8 @@ void qmp_xen_load_devices_state(const char *filename, 
Error **errp)
     migration_incoming_state_destroy();
 }
 
-int load_snapshot(const char *name, strList *exclude, Error **errp)
+int load_snapshot(const char *name, const char *vmstate,
+                  strList *exclude, Error **errp)
 {
     BlockDriverState *bs, *bs_vm_state;
     QEMUSnapshotInfo sn;
@@ -2856,7 +2858,7 @@ int load_snapshot(const char *name, strList *exclude, 
Error **errp)
         return ret;
     }
 
-    bs_vm_state = bdrv_all_find_vmstate_bs(NULL, exclude, errp);
+    bs_vm_state = bdrv_all_find_vmstate_bs(vmstate, exclude, errp);
     if (!bs_vm_state) {
         return -ENOTSUP;
     }
@@ -2943,13 +2945,15 @@ bool vmstate_check_only_migratable(const 
VMStateDescription *vmsd)
 }
 
 void qmp_savevm(const char *tag,
+                bool has_vmstate, const char *vmstate,
                 bool has_exclude, strList *exclude,
                 Error **errp)
 {
-    save_snapshot(tag, exclude, errp);
+    save_snapshot(tag, vmstate, exclude, errp);
 }
 
 void qmp_loadvm(const char *tag,
+                bool has_vmstate, const char *vmstate,
                 bool has_exclude, strList *exclude,
                 Error **errp)
 {
@@ -2957,7 +2961,7 @@ void qmp_loadvm(const char *tag,
 
     vm_stop(RUN_STATE_RESTORE_VM);
 
-    if (load_snapshot(tag, exclude, errp) == 0 && saved_vm_running) {
+    if (load_snapshot(tag, vmstate, exclude, errp) == 0 && saved_vm_running) {
         vm_start();
     }
 }
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index fcde649100..586676e179 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -1091,7 +1091,8 @@ void hmp_loadvm(Monitor *mon, const QDict *qdict)
 {
     Error *err = NULL;
 
-    qmp_loadvm(qdict_get_str(qdict, "name"), false, NULL, &err);
+    qmp_loadvm(qdict_get_str(qdict, "name"),
+               false, NULL, false, NULL, &err);
     hmp_handle_error(mon, err);
 }
 
@@ -1099,7 +1100,8 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
 {
     Error *err = NULL;
 
-    qmp_savevm(qdict_get_try_str(qdict, "name"), false, NULL, &err);
+    qmp_savevm(qdict_get_try_str(qdict, "name"),
+               false, NULL, false, NULL, &err);
     hmp_handle_error(mon, err);
 }
 
diff --git a/qapi/migration.json b/qapi/migration.json
index 2388664077..91173f5b06 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -1630,6 +1630,7 @@
 # @tag: name of the snapshot to create. If it already
 # exists it will be replaced.
 # @exclude: list of block device node names to exclude
+# @vmstate: block device node name to save vmstate to
 #
 # Note that execution of the VM will be paused during the time
 # it takes to save the snapshot
@@ -1641,6 +1642,7 @@
 # -> { "execute": "savevm",
 #      "data": {
 #         "tag": "my-snap",
+#         "vmstate": "disk0",
 #         "exclude": ["pflash0-vars"]
 #      }
 #    }
@@ -1650,6 +1652,7 @@
 ##
 { 'command': 'savevm',
   'data': { 'tag': 'str',
+            '*vmstate': 'str',
             '*exclude': ['str'] } }
 
 ##
@@ -1659,6 +1662,7 @@
 #
 # @tag: name of the snapshot to load.
 # @exclude: list of block device node names to exclude
+# @vmstate: block device node name to load vmstate from
 #
 # Returns: nothing
 #
@@ -1667,6 +1671,7 @@
 # -> { "execute": "loadvm",
 #      "data": {
 #         "tag": "my-snap",
+#         "vmstate": "disk0",
 #         "exclude": ["pflash0-vars"]
 #      }
 #    }
@@ -1676,6 +1681,7 @@
 ##
 { 'command': 'loadvm',
   'data': { 'tag': 'str',
+            '*vmstate': 'str',
             '*exclude': ['str'] } }
 
 ##
diff --git a/replay/replay-snapshot.c b/replay/replay-snapshot.c
index 1351170c67..f0f45a4f24 100644
--- a/replay/replay-snapshot.c
+++ b/replay/replay-snapshot.c
@@ -77,13 +77,13 @@ void replay_vmstate_init(void)
 
     if (replay_snapshot) {
         if (replay_mode == REPLAY_MODE_RECORD) {
-            if (save_snapshot(replay_snapshot, NULL, &err) != 0) {
+            if (save_snapshot(replay_snapshot, NULL, NULL, &err) != 0) {
                 error_report_err(err);
                 error_report("Could not create snapshot for icount record");
                 exit(1);
             }
         } else if (replay_mode == REPLAY_MODE_PLAY) {
-            if (load_snapshot(replay_snapshot, NULL, &err) != 0) {
+            if (load_snapshot(replay_snapshot, NULL, NULL, &err) != 0) {
                 error_report_err(err);
                 error_report("Could not load snapshot for icount replay");
                 exit(1);
diff --git a/softmmu/vl.c b/softmmu/vl.c
index f7c8be8c6a..fbaa326675 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -4452,7 +4452,7 @@ void qemu_init(int argc, char **argv, char **envp)
     register_global_state();
     if (loadvm) {
         Error *local_err = NULL;
-        if (load_snapshot(loadvm, NULL, &local_err) < 0) {
+        if (load_snapshot(loadvm, NULL, NULL, &local_err) < 0) {
             error_report_err(local_err);
             autostart = 0;
             exit(1);
-- 
2.26.2